This invention relates to switches of the type used in controlling fault currents associated with transmission lines in power distribution systems. More particularly, the invention relates to such switches employing chemical propellant actuators.
Fast acting switches are used on power distribution lines for current limiting purposes. Fault currents on high voltage lines, due to ground shorts, for example, can rapidly become enormous and cause serious equipment damage. As transmission voltages rise there is a continuing need in the electric power industry for improved current interrupting switches for use in rapidly controlling fault currents.
Current limiting circuits employ switches which open to divert a fault current through an associated current-suppressive impedance which limits the current to a safe level. Preferably, the circuit is re-established, as rapidly as possible after the source of the fault is eliminated. In the case of short-lived fault sources such as lightning bolts, the opening and closing of interrupter switches is preferably handled automatically. The switches, therefore, should be rapidly responsive to automatic signals, and should produce a large voltage drop sufficient to divert the fault current through the associated protective impedance.
Chemically activated interrupter switches such as those described in application Ser. No. 889,491, filed Mar. 22, 1978, assigned to the assignee of the present invention, provide both rapid contact separation and large voltage drops. As noted above, however, it is desirable to also provide for automatic reclosing of the circuit after the fault has cleared. mechanical deviced for opening and closing switches are generally expensive and are unable to operate with the rapidity desired. Furthermore, switch contacts opened and closed by mechanical actuators generally produce undesirable contact bounce.